1. Field of the Invention
The present invention relates to a lithographic apparatus and a method for manufacturing a device in which measurements are performed for various purposes, such as overlay, critical dimension (CD) and alignment. For the measurements, targets are being used on the substrate, and measurements are executed using radiation of a predefined wavelength (range) and a suitable detector, e.g., using imaging techniques or diffraction techniques.
2. Background Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., including part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In a manufacturing process using a lithographic projection apparatus, a pattern (e.g., in a mask) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist) by the changes of either optical properties or surface physical properties of the resist. Alternatively, the imaging may use a resistless process such as etched grating or nano-imprint technology. Prior to this imaging, the substrate may undergo various procedures, such as priming, resist coating and a soft bake. After exposure, the substrate may be subjected to other procedures, such as a post-exposure bake (PEB), development, a hard bake and measurement/inspection of the imaged features. This array of procedures is used as a basis to pattern an individual layer of a device, e.g., an IC. Such a patterned layer may then undergo various processes such as etching, ion-implantation (doping), metallization, oxidation, chemical-mechanical polishing, etc., all intended to finish off an individual layer. If several layers are required, then the whole procedure, or a variant thereof, will have to be repeated for each new layer. Eventually, an array of devices will be present on the substrate (wafer). These devices are then separated from one another by a technique such as dicing or sawing, whence the individual devices can be mounted on a carrier, connected to pins, etc.
The measurement and inspection after development of the resist (or substrate surface in the case of etching), referred to as in-line because it is carried out in the normal course of processing production substrates, is used, for example, to measure overlay between two sequential processes in the lithography apparatus using measurement targets in the scribe lanes between the devices. Several methods may be used and may include measurement of overlay subsequently in two (perpendicular) directions on the substrate surface, or direct measurement using a complex two dimensional measurement target.
In each process, in general a different piece of scribe lane space is used for the measurement, in order to exclude any possible error due to interference with measurement targets from measurements in previous processes.